The federal government isn't writing the codes. The original codes language was 'high-hazard' and 'low-hazard' and one might make a determination that you could designate a lawn sprinkler system as 'low-hazard' since you aren't reading about the death toll from lawn sprinkler system backflow.

But once you change the language to 'toxic' and 'non-toxic' you've kind of painted the DCVA into a corner, since no manufacturer will claim any ability of a DVCA to deal with toxic backflow. And if any examination of possible contaminants in a sprinkler system is made, there is no reasonable doubt of said contaminants being toxic.

No more than a government document that lists any substance applied by a lawn care company as toxic. But there are those little warning flags they stick on the lawns, before the spray truck drives away.